RFID (radio frequency identification) is an automatic identification technology whereby digital data encoded in an RFID tag is captured by a reader using radio waves. RFID tags consist of an integrated circuit (IC) attached to an antenna, plus some protective packaging (like a plastic card) as determined by the application requirements. Tags also sometimes are called “transponders.” Data is stored in the integrated circuit and sent through the antenna to a reader. Prior art RFID tags are either “passive” (no battery), “semi-passive” or “active.”
Passive RFID tags rely entirely on the reader as their power source. In passive systems, the tag is composed of an antenna and a silicon chip that includes basic modulation circuitry and non-volatile memory. A known technique for communicating with RFID transponders is referred to as “backscatter modulation,” whereby the RFID tags send stored data by modulating the impedance attached to their antenna to reflect varying amounts of an electromagnetic field generated by the RFID reader. An advantage of this communication technique is that the RFID transponders or tags can operate automatically at the frequency of the energizing electromagnetic field, and as a result, the reader may operate at multiple frequencies so as to avoid radio frequency (RF) interference, such as using frequency hopping spread spectrum modulation techniques. The RFID tags may extract their power from the energizing electromagnetic field, thereby eliminating the need for a separate power source. This is also referred to as energy harvesting.
Typically, each RFID tag has an individual code containing information related to and identifying the object associated with the tag. In operation, the reader sends an RF signal to the remote transponder. An antenna at the transponder receives the signal from the reader, backscatter modulates the received signal with data temporarily or permanently stored in the transponder (such as data indicating the identity and contents of the object to which the transponder is attached), thereby producing a sequence of signals in accordance with the transponder's individual code, and reflects this modulated signal back to the reader in order to pass the information contained in the transponder memory to the reader. The reader decodes these signals to obtain the information from the transponder.
Active and semi-passive RFID tags use internal batteries to power their circuits. An active tag also uses its battery to broadcast radio waves to a reader, whereas a semi-passive tag relies on the reader to supply the radio signal for the tag to backscatter. The battery is used to boost the effective operating range of the tag and to support additional features over passive tags, such as operation with lower radio signal strengths and sensing operations that require continuous power. Data collected from tags is then passed through communication interfaces (cable or wireless) to host computer systems and passed to computer systems for interpretation, storage, and action. Alternatively, tag power may be supplied externally, e.g., by means of a car battery.
RFID tags can be read-only (stored data can be programmed and read but not changed remotely), read/write (stored data can be altered or rewritten at a distance), or a combination, in which some data is permanently stored while other memory is left accessible for modification or updating as desired.
RFID tags also include a clocking circuit to enable data to be read and sent to a modulation circuit also located on the tag. A data encoder, also located on the RFID tag retrieves data from the IC chip's data array or memory and sends it to a modulation circuit. Data encoding refers to the process of altering the data bit stream between the time it is retrieved from the RFID's memory and its transmission back to the reader. The various encoding algorithms include NRZ (Non-Return to Zero) Direct; FMO; frequency shift keying; Differential Biphase; Biphase L (Manchester), and others. For an RFID tag of the read/write variety, the tag circuitry includes a memory, a clock, a modulation detector, a data decoder, as well as a means for error detection and circuitry for control and for writing new data into the memory. The reader may also send commands to the tag so that the operations of the tag can be controlled. In addition to reading and writing, additional operations include communication with multiple tags in the field of the reader and selection of special ‘groups’ of tags. RFID tags, including passive tags, may also perform encryption operations to participate in mutual authentication processes as well as protection of data and prevention of unauthorized operations.
A reader (often referred to as an RFID interrogator) is basically a radio frequency (RF) transmitter and receiver, controlled by a microprocessor or digital signal processor. The reader, using an attached antenna, captures data from the RFID tag, then passes the data to a computer for processing. As with RFID tags, readers come in a wide range of sizes and offer different features. Readers can be affixed in a stationary position or can be portable, including hand-held.
The use of RFID has been widely accepted for tracking and managing movable equipment, vehicles, containers, items in the supply chain and other such applications. Specific examples of common applications are the use of RFID to manage railcar equipment, for electronic toll collection, vehicular access control, electronic vehicle registration, highway traffic monitoring and truck fleet management. These applications usually require an interrogation distance, or range, of tens of meters. For use of radio signals, this range translates into a requirement to use UHF or S-band microwave signals. Traditional RFID tags have been constructed from a handful of components. Operational power was achieved by an attached battery or by rectification of the interrogating RF signal. The battery-powered option permitted longer ranges at the expense of increased cost and a defined limited life. Tags without batteries are of lower cost, essentially unlimited life, but of shorter range.
Developments within the last several years have given rise to RFID tags using a single integrated circuit attached to an antenna and operating in the UHF or S-Bands (typically in the range of 400 MHz to 3 GHz). Without batteries, those newer tags could be made smaller, less expensive, yet high performance in terms of function and memory. Interrogation range is adequate in countries where radio regulations permit sufficient RF power transmission to power the tags. The primary drawbacks of this new generation of RFID tags is that some country's radio regulations do not permit sufficient range, and in countries where higher powers and increased ranges are allowed, the range was adequate but limiting.